What does the Bible say about man's sinfulness?

The Bible teaches that man is inherently sinful as a result of Adam's fall, which is evidenced in Romans 5:12, where sin entered the world through one man, and death through sin. This sinfulness is not only a condition but also an active rebellion against God. In passages like 2 Samuel 3, we are reminded of the strife that exists as a picture of the continuous warfare between our flesh and spirit. This highlights the fallen nature of humanity and the necessity for redemption through Christ, the only sinless man.